It has been known to place a temperature-sensing element such as a thermistor in heat transfer relation with a thyristor by mounting it on the thyristor case. Such thermistor has been connected in the thyristor firing control circuit to regulate the thyristor current flow for temperature-compensation purposes, that is, to maintain the thyristor temperature below a damaging value. It has also been known to mount a thermistor in heat transfer contact with a semi-conductor device and to connect such thermistor in the gate circuit of the semiconductor to prevent excessive junction temperatures. Also, it has been known to mount a thermally-sensitive thyristor in heat transfer relation with a load and connect it to control the load-energizing thyristor. Furthermore, it has been known to gate control a thyristor by a light source acting on a photo-sensitive element connected in the thyristor gate circuit.
While these prior systems have been useful for their intended purposes, this invention relates to improvement thereover.